Al Jazeera searched the database of the International Consortium of Investigative Journalists (ICIJ) that includes 11.5 million documents leaked from the Panama-based law firm Mossack Fonseca, and found Safdar's details.

Safdar was listed as the beneficiary of Nescoll Limited, an offshore company registered in British Virgin Islands. Her brother Hussain Nawaz Sharif was listed as the signatory.

In all, Sharif's daughter Maryam and sons Hasan and Hussain owned at least three off-shore holding companies registered in the British Virgin Islands, the leaked documents show.

According to the ICIJ, a non-profit group in the United States, these firms were involved in the purchase and mortgage of at least $13.8m in UK properties. One of the holding companies also bought shares in another, Liberia-based, company for $11.2m in August 2007, the documents show.

Owning off-shore companies is not illegal in Pakistan, but the Sharifs are being challenged on the source of the funds. Opposition politicians allege the funds were gained through corrupt practices during Sharif's previous two stints as prime minister in the 1990s.

The Panama Papers was one of the biggest leaks in history [ICIJ]

Allegations of corruption against the Sharif family are being heard in Pakistan's Supreme Court.

He said he was not holding any offshore companies. Sharif also claimed that he had paid tax and declared all of his assets in 2013.

The Panama Papers leak revealed how Mossack Fonseca allegedly helped current and former world leaders, as well as businessmen, criminals, celebrities and sports stars, evade or avoid tax via anonymously-owned shell companies and offshore accounts.

The story garnered wall-to-wall coverage and dominated front pages of newspapers across the world.

ICIJ coordinated the reporting, with 376 journalists from 109 news organisations and 76 countries poring over the files.